The effects of heavy rainfall on sedimentation in the tidal salt marsh of Suncheon bay, south Korea

Abstract

Tide observations, geographic surveys, sediment composition and sediment accretion rate monitoring were conducted to investigate the relationship between general pattern changes and control factors of the accretion rate at 10 localities of the tidal salt marsh of Suncheon bay over 2 years (June 2007~May 2009). The tidal flat is a meso tidal flat with a mean range of 217.8 cm and has a southwest to northeast direction tidal current with an average velocity of 26.57 cm/sec. Flood strength (100 cm/sec) appeared to dominate over ebb strength (60 cm/sec). The substrate sediments of tidal salt marsh that are distributed between the mean sea level and the high water of ordinary spring tide, are mainly composed of silt (37.98%), and clay (60.45%), and have a net annual accretion rate of 28.88 mm/yr. The net annual accretion rate of areas effect by the tidal salt marsh creeks compared to areas unaffected is 8.7 mm/yr, and 42.3 mm/yr, respectively. The tidal salt marsh substrate sediments in Suncheon bay are deposited and supplied by flood tidal currents. The high concentrations of suspended sediments were a result of the muddy tidal flat and waves generated within the bay by strong winds or storms. During the deposition of substrate sediments, the sheet-flow formed by the heavy rainfall promotes the detachment of substrate particles and causes mass scouring, or re-suspension of particles, and transports sediments back into the tidal flat. Heavy rainfall may lead to enhanced tidal salt marsh-tidal mud flat sediment cycling. The variation in patterns of average annual accretion rate affected by the heavy rainfall can be divided into three stages: the Low Stage (June 2007~February 2008; 8.8 mm on average), which is the lowest period of accretion rate, the Recovery Stage (February 2008~October 2008), which is the period of rapid increase in accretion rate from 14.93 mm to 49.47 mm with anaverage of 33.02 mm, and the High Stage (November 2008~May 2009), which is aperiod of h